Capacitors for HP filters in tube amps recommendations?

Excellent @pragmasi, exactly the kind of information I was hoping for! And lots of it!! Pure ee considerations and concerns, very much aligned with the kind of thinking that went into the design of the amps. No intent or desire to disparage audiophile language and concerns, but you gotta get the ee stuff right first ;-) .

Yes, having the caps matched to 1% is a very high priority (perhaps THE priority). I’ve seen the term "time constants" many times over the years, but never took the time to educate myself on what it means. Perhaps I should do so now! I’m also familiar with the term "parasitic", and DO understand it. It’s bad, right? ;-) . I’ll look up Doug Self (I’m familiar with the name) and his research.

I’m going to try and reach RM (the designer and maker of the amps), He may have the caps I need in his parts inventory. He encourages the installation of caps on the input jacks of his amps as a way to create a 1st-order filter for partnering the amp/speaker with a sub. I’m sure he views the question of cap "sound" just as do you---a matter of their electrical characteristics in any given application.

Thanks again for all your time and help @pragmasi. It is very much appreciated, and of great value and use to me---Eric.

@ramlabs, Roger, baby, where are ya?! When you have time, could you look for my email from last week? I'll call you Monday morning.

I just realised the capacitors in the link above are 5% tolerance, shouldn't be too hard to find 1% ones though... in the UK they are available from both Farnell and RS Components.

I’m also familiar with the term "parasitic", and DO understand it. It’s bad, right? ;-)

Parasitic properties are the characteristics of the 'real world' component that deviate from the ideal. An example in this case would be the capacitor's inductance, that is directly related to lead length so a large axial resistor will present greater inductance than a small radial cap with short leads. Whether anyone can hear the difference is another matter but if you can avoid it then why not.

In reality you could get a good result using 1% polystyrene or 1% polypropylene, the former are smaller and less expensive... it's less clear whether the better spec in terms of parasitics would make an audible improvement.

Hope the project works out well whichever you choose.

I noticed that too. There are some cap vendors who match them in pairs, and Parts Connexion offers hand picked caps that are 1/2 or 1/4 of the factory tolerance figure, but they sell only "audiophile" brands. I think Michael Percy offers the polystyrene caps he sells (Rel and Multicap, each about $5/ea) matched to 1%, but to each other, not tolerance. The caps you provided the link to are sold on ebay, but I’m not going there!

Something suddenly occurred to me last night: as I mentioned, one of the amps has balanced/XLR inputs, requiring a cap for each leg of each XLR. What I forgot was that while the input is 30k ohms, each leg is of course half that---15k. So on that amp I need not .03uF (three .01 caps) per input jack, but rather .06uF (six .01uF caps!) for each leg of the XLR connection! Oy!

@pragmasi, I took a look at the product description of the B4 cross-over (one of which I own) on the First Watt website, and in it Nelson Pass mentions he used Wima Polypropylene film caps in all the filters. If they’re good enough for Nelson.....

I then went on the Wima site, and I’ll be darned: they offer a .01uF poly cap (model no. FKP 2) with a range of tolerances, 1.5% being the lowest "regularly" available, but 1% available if requested.

Mouser sells the 1% version for cheap ($2.11/ea, $17.10/for 10), so I have my caps. For the 100k/80Hz amp, anyway. I’m thinking I’ll just use the B4 on the 30k/175Hz amp, as soldering .12uF onto each XLR may be just too much!

Thanks again for your advice, it was of great help.